1. Field of the Invention
The invention relates to a device for controlling the time of actuation of a spring which may be incorporated, for example, in a disposable safety syringe or catheter.
2. Brief Description of the Prior Art
Springs are commonly used as a power source for the actuation of an auxiliary component or device. However, springs have one characteristic which is unattractive in many applications. The amount of force which is generated by the spring when it is moved between stressed and free states is a largely linear function of the amount by which the spring has been compressed or expanded from its free state. Accordingly, when the spring is released, the spring generates its maximum amount of force at the instant of release, and the force declines linearly as the spring recovers to its free state.
In many applications, this sudden acceleration is undesirable. For example, in U.S. Pat. No. 5,053,010, entitled "Safety Syringe with Retractable Needle", issued Oct. 1, 1991, there is shown and disclosed an improved safety syringe with retractable needle which allows retraction of the needle into a hollow plunger by forward pressure on the plunger after fluid is driven from the syringe into the patient. The syringe includes a hollow plunger which is inserted into one end of a cylindrical barrel and a hollow needle attached to the other end of the barrel. Actuation of the plunger subsequent to injection of the fluid within the barrel into the patient will cause the compressive bias within a spring mechanism to be applied against a carrier for the shifting of the needle into the interior of the hollow plunger. If liquid, such as medicine, still is contained within the interior of the hollow needle during the retraction step, the sudden acceleration of the needle in a backward-like direction into the interior of the plunger may, depending upon on the amount, viscosity, temperature, pressure and other variables, cause or contribute to considerable quick ejection out of the open end of the needle of such fluid, resulting in spillage onto the patient, operator, or floor immediate the area of positioning of the syringe. A similar situation could occur when the device to be actuated by the spring biasing mechanism is provided in the form of a catheter. The present invention addresses the problems set forth above.